可调谐射频磁探针研究

A tunable radio-frequency magnetic probe

提出了一种利用可调谐变压器提高磁探针灵敏度的方法。可调谐射频变压器采用在原线圈并联可变电容及在副线圈串联可变电容的结构,用平面分立式法拉第屏蔽抑制变压器原、副线圈间寄生的容性耦合。测量结果表明:在采用中心抽头变压器及法拉第屏蔽的情况下,磁探针的容性耦合大幅度降低;当调节并联或串联电容时,磁探针输出电压均出现共振现象;调节并联电容得到的共振输出电压高于调节串联电容时的对应值;在典型条件下,共振输出电压幅值比无可变电容磁探针提高了约一个量级。建立了探针电路模型,计算结果与测量结果符合较好。

A tunable center-tapped transformer is proposed to improve the sensitivity of an RF （radio-frequency） magnetic probe. The transformer involves two variable capacitors： one is parallel with the primary winding and another is in series with the secondary winding. In addition, a planar faraday shield, which consists of two discrete slotted metal plates, is installed between two windings to suppress the electrostatic coupling. It is found that the capacitive coupling of the probe is effectively reduced and the resonance of the probe output voltage can be achieved by tuning the parallel or the series capacitor. It is also found that the resonant output-voltage obtained by tuning the parallel capacitor is larger than that with the series capacitor, and the largest output under typical conditions is higher than the conventional probe by one order of magnitude. A circuit model of the tunable RF magnetic probe is established and the calculation results are in good agreement with the measurements.